Heat Gun with Self-Cooling System

ABSTRACT

A heat gun includes a head portion defining a flow passage and including a windshield disposed at an outlet end of the flow passage. The windshield includes a first partition and a shield. The first partition has opposing first and second sides. The first side aligns a first phantom line. The shield includes a first, second, and third through hole. The first through hole is located on a right side of the first phantom line. The second through hole is located on a left side of the first phantom line. The third hole includes a portion located on the right side of the first phantom line and a portion located on the left side of the first phantom line.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a heat gun and, particularly, to a heatgun with a self-cooling system.

2. Description of the Related Art

EP 1795803 A2 shows a modular gas burning hand tool including an mainbody (3), an ignite gas conduit (7) extending longitudinally in the mainbody (3) for circulating gas, a grip handle (5), a burner part (9)including a hollow body extending from the main body (3) andcommunicating with the ignite gas conduit (7) and including agas-powered unit (11) disposed at an end of the hollow body. The burnerpart (9) has a junction part (13) opposite the gas powered unit (11).The main body (3) also has a junction part (15). The junction parts (13,15) are adapted to releasably connect to one another.

It is known for conventional gas heat guns to use high pressure gas andto incorporate venturi tubes to mix the gas. The high pressure gas isspewed at a high velocity out of a gas nozzle in the venturi tube. Thegas causes outside air to flow to the venturi tube and a chamber fromwhich a flame exits to achieve an appropriate ratio of gas mixture andto increase the amount of the gas mixture. The venturi tube includes ahollow recifying mixing chamber at another end. The mixing chamber isshrouded by a flow-rectifying cover that is configured to control theflow speed and distributability of the gas mixture as well as preventingthe backward propagation of flame. Moreover, the greater width of aflame exit end of the gas heat gun, the easier the user can operate thegas heat gun to heat the target precisely and to heat large areasquickly.

However, conventional high power gas heat guns suffer problems,including:

1. Flame flowing out of the flame exit end is not evenly distributed andtherefore doesn't apply heat to a surface evenly.

2. Mixing and dispensing gas unevenly result in a poor combustion, whichnot only reduces efficiency and wastes gas, but also produce too muchnoxious carbon monoxide (CO) and nitrogen oxide (NOx).

3. The temperature of the flame exit end is very high and a large amountof heat is concentrated. Furthermore, heat radiates and conducts, andtherefore the chamber, which includes the flame exit end, is hot andoften reaches a temperature above 100 degrees Centigrade. Therefore,there is a high risk that the user gets burned inadvertently.

4. The flow-rectifying cover has an exit being too small, which resultsin substantial pressure losses, a flow capacity decrease overall, and adifficulty to increase heat power.

5. High pressure gas and the gas mixture create much turbulence in themixing chamber and the flow-rectifying cover and induce noise.

6. Rectifying flows unduly causes the flame at the flame exit end toflow at a low speed. Since the flame spreads linearly mostly, if theflame flows at a speed which is too low, the flame is susceptible todistortion under thermal buoyant effects. Thus, it is difficult to aimthe gas heat gun at the target precisely. The flame is also easilyaffected by air currents when the gas heat gun is used in an outsideenvironment. Thus, it is difficult to operate and aim the gas heat gunat the target precisely in a wind environment and especially if the windvaries directions. Furthermore, when the flame moves against the wind,the flame, which flows too slow, may burn backward toward the user.

7. If gas is mixed and dispensed unsteadily, a suitable pressure rangefor supplying gas becomes limited, and the chance to ignite the gas issubstantially reduced.

The conventional mixing chamber is fan-shaped and varies regularly incross section along a center axis of the venturi tube. In order to speedup operations, it is necessary to increase areas that can be heatedinstantaneously as well as heat power. Thus, an exit of the mixingchamber which has a narrow width is not desired. Increasing the width ofthe exit of the mixing chamber, however, makes it more difficult tocontrol flows at the exit at the same speed. In fact, flows at two sidesof the exit flow faster and flows in the middle of the exit flow slower(see FIG. 17). If reducing the width of the exit of the mixing chamber,areas that can be heated is smaller. If increasing heat power, heatconcentrates in a small region and results in local overheating. Ifincreasing a distance between the gas heat gun and the target, thermalbuoyant force and air flow disturbance make it difficult for the user toaim the gas heat gun at areas to be heated. Therefore, a high power gasheat gun that allows a user heat a target precisely and evenly includesa wide flame exit and flame exits at high speed.

In addition to flow noise and the phenomenon that the temperature at thetwo sides are higher, the flame is nearly transparent, and therefore itis hard to perceive the direction of heat transfer. This causes the userto have a poor aim of the target and where the gas heat gun aims is notexactly where the user wants to heat. Furthermore, since the flows arenot at the same speed, an increase of heat capacity results inincomplete combustions at the two sides, and trying to use flow guidesto control flows, however, imposes frictional forces on the flows andreduces overall flow capacity and efficiency.

Since large amount of heat is concentrated at the flame exit end, thetemperature is very high, due to heat radiation and conduction, and isoften above 100 degrees Centigrade. Therefore, there is a high risk thatthe user gets burned inadvertently. After the flame stops, it also takesquite a while to dissipate heat and cool the temperature down withrespect to the ambient temperature and, since the user doesn't know whenthe gas heat gun has cooled, it is easy that he or she can get burnedinadvertently.

FIG. 16 is a partial, cross-sectional view of a conventional gas heatgun. As set forth, the gas heat gun includes a device 11′ from which gasburns. The device 11′ includes a net and a main body defining a tube incircular cross-section. When gas flows in the tube, it flows faster atthe center than at the edges. The gas will flow pass the main body andinto a burner part 9′. Likewise, the gas flows faster at the center ofthe burner part 9′ than at the edges of the burner part 9′. The gas inthe burner part 9′ will contact the device 11′. The device 11′ willobstruct and deflect the gas. FIG. 16 shows that after the gas isobstructed by the device 11′, it is partially deflected and flows towardtwo sides of the burner part 9′ in opposing directions, and consequentlyflow capacity at the two sides of the burner part 9′ is more and flowcapacity in the middle of the burner part 9′ is lesser. As a result, thetemperature at the two sides is higher than the temperature in themiddle, and the gas heat gun does not give out even heat and uniformtemperature. Furthermore, the burner part 9′ is very hot, but the usercan't tell by appearance, and therefore it is easy that he or she canget burned inadvertently.

The present invention is, therefore, intended to obviate or at leastalleviate the problems encountered in the prior art.

SUMMARY OF THE INVENTION

According to the present invention, a heat gun with a self-coolingsystem includes a head portion defining a flow passage and including awindshield. The flow passage extends longitudinally along an axis andhas an inlet end at one end and an outlet end at another end opposingthe inlet end. The windshield is disposed at the outlet end of the flowpassage and includes a first partition and a shield. The first partitionhas opposing first and second sides extending parallel to the axis. Thefirst side aligns a first phantom line. The shield extends transverselyto the axis and is disposed adjacent to an end of the first partitionwhich is opposite to the flow passage. The shield includes a first,second, and third through hole. The first through hole is located on aright side of the first phantom line. The second through hole is locatedon a left side of the first phantom line. The third hole including aportion located on the right side of the first phantom line and aportion located on the left side of the first phantom line.

There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are additionalfeatures of the invention that will be described hereinafter and whichwill form the subject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein are for the purpose of description and should not beregarded as limiting.

As such, those skilled in the art will appreciate that the conception,upon which this disclosure is based, may readily be utilized as a basisfor designing of other structures, methods and systems for carrying outthe several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

Further, the purpose of the foregoing abstract is to enable the publicgenerally, and especially the scientists, engineers and practitioners inthe art who are not familiar with patent or legal terms or phraseology,to determine quickly from a cursory inspection the nature and essence ofthe technical disclosure. The abstract is neither intended to define theinvention, which is measured by the claims, nor is it intended to belimiting as to the scope of the invention in any way.

Other objectives, advantages, and new features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat gun with a self-cooling system inaccordance with a first embodiment of the present invention.

FIG. 2 is an exploded perspective view of a head portion of the heat gunof the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of the head portion of the heat gun ofthe first embodiment of the present invention.

FIG. 4 is another cross-sectional view of the head portion of the firstembodiment of the heat gun of the present invention.

FIG. 5 is a partial, enlarged view of FIG. 4.

FIG. 6 is a cross-sectional view of the heat gun of the first embodimentof the present invention, taken from a line extending transversely to anaxis L that is shown in FIG. 3.

FIG. 7 is a cross-sectional view of the heat gun of the first embodimentof the present invention, taken from another line extending transverselyto the axis L that is shown in FIG. 3.

FIG. 8 is a cross-sectional view illustrating the heat gun of the firstembodiment of the present invention in operation, with arrows indicatingflows.

FIG. 9 is another cross-sectional view illustrating the heat gun of thefirst embodiment of the present invention in operation, with solid linesillustrating heat.

FIG. 10 is another cross-sectional view illustrating the heat gun of thefirst embodiment of the present invention, with arrows indicating flows,and with solid lines illustrating heat.

FIG. 11 is a perspective view of a heat gun with a self-cooling systemin accordance with a second embodiment of the present invention.

FIG. 12 is an exploded perspective view of a head portion of the heatgun of the second embodiment of the present invention.

FIG. 13 is a cross-sectional view of the head portion of the heat gun ofthe second embodiment of the present invention.

FIG. 14 is a cross-sectional view illustrating the heat gun of thesecond embodiment of the present invention in operation, with arrowsindicating flows.

FIG. 15 is a partial, enlarged view of FIG. 14.

FIG. 16 is a cross-sectional view of a conventional heat gun.

FIG. 17 is a thermal image of conventional heat gun in operation.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 10 show a heat gun 10 with a self-cooling system inaccordance with a first embodiment of the present invention.

The heat gun 10 includes a head portion 20. The head portion 20 definesa flow passage 21. The flow passage 21 extends longitudinally along anaxis L. The flow passage 21 has an inlet end 211 at one end and anoutlet end 212 at another opposite end. The flow passage 21 includes aninlet portion 213, an outlet portion 214 and a flow guiding portion 215disposed between the inlet and outlet ends 211 and 212.

The inlet portion 213 has a radial cross-sectional area about the axisL. The outlet portion 214 has a radial cross-sectional area about theaxis L and which is greater than 0.8 times and smaller than 1.2 times ofthe radial cross-sectional area of the inlet portion 213. The radialcross-sectional area of the inlet portion 213 is circular in shape. Theradial cross-sectional area of the outlet portion 214 is quadrilateralin shape.

The outlet portion 214 is formed with two long sides 216 and two shortsides 217. The two long sides 216 are opposite one another. The longside 216 extends lengthwise of the outlet portion 214 and in a directiontransverse to the axis L a length D. The two short sides 217 areopposite one another. The two short sides 217 extend between the twolong sides 216. The short side 217 extends widthwise of the outletportion 214 and in a direction transverse to the axis L a width W. Thelength D is greater than a maximum width of the inlet end 211. Themaximum width of the inlet end 211 extends in the lengthwise directionof the outlet portion 214. The width W is smaller than the maximum widthof the inlet end 211. In addition, the two surfaces 221 are spaced at adistance greater than or equal to the width W.

The flow passage 21 includes two flow guiding protrusions 22 disposed atthe flow guiding portion 215. The flow guiding protrusions 22 includetwo outer peripheries facing oppositely and converging toward oneanother in a direction from outlet portion 214 to the inlet portion 213.Each of the two outer peripheries of the two flow guiding protrusions 22has a nonplanar contour. The two flow guiding protrusions 22 aredisposed oppositely.

The head portion 20 includes two surfaces 221 disposed oppositely, andthe two flow guiding protrusions 22 protrude between the two surfaces221. The two surfaces 221 are disposed parallel to one another, orotherwise, incline from each other such that an included angle formedtherebetween is greater than 0 degrees and less than 10 degrees. Whenthe two surfaces 221 are inclined, a distance between ends of the twosurfaces 221 which are adjacent to the inlet portion 213 is greater thana distance between ends of the two surfaces 221 which are adjacent tothe outlet portion 214.

The flow guiding portion 215 is disposed between the inlet and outletportions 213 and 214. The flow guiding portion 215 is partitioned by thetwo flow guiding protrusions 22 and defines a first flow region 23 whichextends along a first extension axis C1, a second flow region 24 whichextends along a second extension axis C2 and a third flow region 25. Thefirst and second extension axes C1 and C2 are symmetrical about the axisL. The first extension axis C1 intersects the second extension axis C2at an included angle A greater than 60 degrees and smaller than 160degrees. The third flow region 25 is disposed between the two flowguiding protrusions 22. The first and third flow region 23 and 25 aredisposed on opposite sides of one of the two flow guiding protrusions22. The second and third flow regions 24 and 25 are disposed on oppositesides of another of the two flow guiding protrusions 22. The third flowregion 25 includes a side connected to the first flow region 23 and anopposite side connected to the second flow region 24. The first flowregion 23 extends from a first end which is adjacent to the inletportion 213 to a second end which is adjacent to the outlet portion 214and has a gradually reduced cross-section from the first end to thesecond end.

The first flow region 23 has a middle portion which is in the middlebetween the inlet portion 213 and the outlet portion 214 and which has aradial cross-section about the first extension axis C1 greater than 0.25times and smaller than 0.4 times of a radial cross-section of the inletportion 213 about the axis L. The second flow region 24 extends from afirst end which is adjacent to the inlet portion 213 to a second endwhich is adjacent to the outlet portion 214 and has a gradually reducedcross-section from the first end to the second end. The second flowregion 24 has a middle portion which is in the middle between the inletportion 213 and the outlet portion 214 and which has a radialcross-section about the second extension axis C2 greater than 0.25 timesand smaller than 0.4 times of the radial cross-section of the inletportion 213.

Furthermore, the first flow region 23 has a maximum radialcross-sectional area about the first extension axis C1 which is ⅓ of amaximum radial cross-sectional area of the inlet portion 213 about theaxis L. The second flow region 24 has a maximum radial cross-sectionalarea about the second extension axis C2 which is ⅓ of the maximum radialcross-sectional area of the inlet portion 213 about the axis L. Thefirst flow region 23 has a minimum radial width about the firstextension axis C1 greater than a minimum radial cross-section of thethird flow region 25 about the axis L. The second flow region 24 has aminimum radial width about the second extension axis C2 greater than theminimum radial width of the third flow region 25 about the axis L.

The head portion 20 cooperates with a windshield 30 to improve floweffects. The windshield 30 is disposed at the outlet end 212 of the flowpassage 21. The windshield 30 includes a first partition 31, a secondpartition 32, and a shield 33. The first and second partitions 31 and 32each extend parallel to the axis L from an end adjacent to the outletportion 214 to another end. The first partition 31 has opposing firstand second sides 311 and 312 extending parallel to the axis L. The firstside 311 aligns a first phantom line P1. The first side of the first andsecond partitions 31 and 32 are planar. The second partition 32 hasopposing first and second sides 321 and 322 extending parallel to theaxis L. The second side 322 aligns a second phantom line P2. The secondside of the first and second partitions 31 and 32 are planar. The firstsides 311 and 321 of the first and second partitions 31 and 32 faceoppositely. The second partition 32 is disposed at the outlet end 212 ofthe flow passage 21 and in a spaced relationship with the firstpartition 31. The first and second partitions 31 and 32 are spaced at adistance greater than the width W. The shield 33 includes a fourth andfifth through hole 334 and 335. The fourth through hole 334 is locatedon a right side of the second phantom line P2. The fifth through hole335 includes a portion located on the right side of the second phantomline P2 and a portion located on a left side of the first phantom lineP1.

The shield 33 extends transversely to the axis L and is disposedadjacent to another ends of the first and second partitions 31 and 32.The shield 33 includes a first, second, third, fourth, and fifth throughhole 331, 332, 333, 334, and 335. The first through hole 331 is locatedon a right side of the first phantom line P1. The first through hole 331of the shield 33 is located between first and second phantom lines P1and P2. The second through hole 332 is located on a left side of thefirst phantom line P1. The third through hole 333 includes a portionlocated on the right side of the first phantom line P1 and a portionlocated on the left side of the first phantom line P1.

FIGS. 13 through 15 show a heat gun 10 a with a self-cooling system inaccordance with a second embodiment of the present invention, and thesame numbers are used to correlate similar components of the firstembodiment, but bearing a letter a. The heat gun 10 a includes a headportion 20 a. The head portion 20 a defines a flow passage 21 a. Theflow passage 21 a extends longitudinally along an axis L. The flowpassage 21 a has an inlet end 211 a at one end and an outlet end 212 aat another opposite end. The flow passage 21 includes an inlet portion,an outlet portion and a flow guiding portion disposed between the inletand outlet ends. The radial cross-sectional area of the inlet portion iscircular in shape. The radial cross-sectional area of the outlet portionis annular in shape.

The head portion 20 a cooperates with a windshield 30 a to improve floweffects. The windshield 30 a is disposed at the outlet end 212 a of theflow passage 21 a. The windshield 30 a includes a first partition 31, asecond partition 32, and a shield 33 a. The first partition 31 a hasopposing first and second sides 311 a and 312 a extending parallel tothe axis L. The first and second sides 311 a and 312 a of the firstpartition 31 a are arcuate. The windshield 30 a includes a secondpartition 32 a cooperating with the first partition 31 a. The secondpartition 32 a has opposing first and second sides 321 a and 322 aextending parallel to the axis L. The first side 321 a aligns a secondphantom line P2. The first sides 311 a and 321 a of the first and secondpartitions 31 a and 32 a face oppositely. The second partition 32 a isdisposed at the outlet end 212 a of the flow passage 21 a and in aspaced relationship with the first partition 31 a. The shield 33 aincludes a first, second, third, fourth, and fifth through hole 331 a,332 a, 333 a, 334 a, and 335 a. The first through hole 331 a of theshield 33 a is located between first and second phantom lines P1 and P2.The first through hole 331 a is located on a right side of the firstphantom line P1. The second through hole 332 a is located on a left sideof the first phantom line P1. The third hole 333 a includes a portionlocated on the right side of the first phantom line P1 and a portionlocated on the left side of the first phantom line P1. The fourththrough hole 334 a is located on a right side of the second phantom lineP2. The fifth through hole 335 includes a portion located on the rightside of the second phantom line P2 and a portion located on a left sideof the second phantom line P2.

The head portion 20 a includes an air amplifier 22 a for inducingexternal air flow. The inlet end 211 a is formed at an end of the airamplifier 22 a. Further, a tube defines the flow passage 21 a. The tubeis circular in shape. The air amplifier 22 a defines a channel having afirst opening and a second opening opposite the first opening. The firstopening has a first radial cross-sectional area about the axis L. Thesecond opening has a second radial cross-sectional area about the axis Lsmaller than the first radial cross-sectional area.

In view of the forgoing, hot air flows mainly between the first andsecond partitions 31, 31 a, 32, 32 a and out of the head portions 20 and20 a through the first through holes 331 and 331 a. Hot air also flowsout of the head portion 20 and 20 a through the portion of the thirdthrough holes 333 and 333 a that is located on the right side of thefirst phantom line P1 and the portion of the fifth through hole 335 and335 that is located on the left side of the second phantom line P2. Whenhot air flows through the set forth portions of the third through holes333 and 333 a, it creates a strong negative pressure, thereby inducingexternal air flow into the head portions 20 and 20 a through the portionof the portion of the third through holes 333 and 333 a that is locatedon the left side of the first phantom line P1 and the portion of thefifth through hole 335 and 335 a that is located on the right side ofthe second phantom line P2. External air circulates in a region that islocated on the left side of the first phantom line P1 and in anotherregion that is located on the right side of the second phantom line P2,thereby ii cooling the head portions 20 and 20 a and keeping the itstemperature less than 40 degree Celsius to preventing burning a user ofthe heat gun.

Furthermore, the head portions 20 and 20 a greatly reduce the likelihoodthat flows flowing backward and turbulence, thereby improving combustionefficiency, as well as lowering noise and preventing pressure drops.Furthermore, the head portions 20 and 20 a allow higher flow capacitywhen compared with conventional head portion designs as well as heat todistribute evenly and greater pressure range. Consequently, heatingconditions can be easily controlled. Even if the pressure varies, thechance to ignite the gas is not affected.

The foregoing is merely illustrative of the principles of this inventionand various modifications can be made by those skilled in the artwithout departing from the scope and spirit of the invention.

What is claimed is:
 1. A heat gun with a self-cooling system comprising:a head portion defining a flow passage which extends longitudinallyalong an axis and has an inlet end at one end and an outlet end atanother end opposing the inlet end and; a windshield disposed at theoutlet end of the flow passage and including a first partition and ashield, wherein the first partition has opposing first and second sidesextending parallel to the axis, wherein the first side aligns a firstphantom line, wherein the shield extends transversely to the axis and isdisposed adjacent to an end of the first partition which is opposite tothe flow passage, and wherein the shield includes a first, second, andthird through hole, with the first through hole located on a right sideof the first phantom line, with the second through hole located on aleft side of the first phantom line, and with the third through holeincluding a portion located on the right side of the first phantom lineand a portion located on the left side of the first phantom line.
 2. Theheat gun as claimed in claim 1, wherein the flow passage includes anoutlet portion disposed between the inlet and outlet ends, wherein theoutlet portion is formed with two long sides and two short sides, withthe two long sides opposite one another, and with the two short sidesopposite one another, wherein the short side has a width extending in adirection transverse to the axis, wherein the windshield includes asecond partition cooperating with the first partition, wherein thesecond partition has opposing first and second sides extending parallelto the axis, wherein the first side aligns a second phantom line,wherein the first sides of the first and second partitions faceoppositely, wherein the second partition is disposed at the outlet endof the flow passage and in a spaced relationship with the firstpartition, wherein the first and second partitions are spaced at adistance greater than the width, wherein the first through hole of theshield is located between first and second phantom lines, and whereinthe shield includes a fourth and fifth through hole, with the fourththrough hole located on a right side of the second phantom line, andwith the fifth through hole including a portion located on the rightside of the second phantom line and a portion located on a left side ofthe second phantom line.
 3. The heat gun as claimed in claim 2, whereinthe long side has a length extending in a direction transverse to theaxis, wherein the length is greater than a maximum width of the inletend, and wherein the width is smaller than the maximum width of theinlet end.
 4. The heat gun as claimed in claim 2, wherein the flowpassage includes an inlet portion disposed between the inlet and outletends, wherein the outlet portion has a first radial cross-sectional areaabout the axis and the inlet portion has a second radial cross-sectionalarea about the axis respectively, and wherein the first radialcross-sectional area is greater than 0.8 times and smaller than 1.2times of the second radial cross-sectional area.
 5. The heat gun asclaimed in claim 4, wherein the first radial cross-sectional area iscircular in shape, and wherein the second radial cross-sectional area isquadrilateral in shape.
 6. The heat gun as claimed in claim 5, whereinthe flow passage includes a flow guiding portion disposed between theinlet and outlet ends, wherein the flow guiding portion includes twoflow guiding protrusions disposed oppositely, wherein the flow guidingportion is partitioned by the two flow guiding protrusions and defines afirst flow region which extends along a first extension axis, a secondflow region which extends along a second extension axis and a third flowregion, wherein the third flow region is disposed between the two flowguiding protrusions, wherein the first and third flow regions aredisposed on opposite sides of one of the two flow guiding protrusions,wherein the second and third flow regions are disposed on opposite sidesof another of the two flow guiding protrusions, wherein the third flowregion includes a side connected to the first flow region and anopposite side connected to the second flow region, wherein the firstflow region extends from a first end which is adjacent to the inletportion to a second end which is adjacent to the outlet portion and hasa gradually reduced cross-section from the first end to the second end,wherein the first flow region has a middle portion which is in themiddle between the inlet portion and the outlet portion and which has aradial cross-section about the first extension axis greater than 0.25times and smaller than 0.4 times of a radial cross-section of the inletportion about the axis, wherein the second flow region extends from afirst end which is adjacent to the inlet portion to a second end whichis adjacent to the outlet portion and has a gradually reducedcross-section from the first end to the second end, wherein the secondflow region has a middle portion which is in the middle between theinlet portion and the outlet portion and which has a radialcross-section about the second extension axis greater than 0.25 timesand smaller than 0.4 times of the radial cross-section of the inletportion.
 7. The heat gun as claimed in claim 6, wherein the first flowregion has a maximum radial cross-sectional area about the firstextension axis which is ⅓ of a maximum radial cross-sectional area ofthe inlet portion about the axis, and wherein the second flow region hasa maximum radial cross-sectional area about the second extension axiswhich is ⅓ of the maximum radial cross-sectional area of the inletportion about the axis.
 8. The heat gun as claimed in claim 7, whereinthe first flow region has a minimum radial width about the firstextension axis greater than a minimum radial cross-section of the thirdflow region about the axis, and wherein the second flow region has aminimum radial width about the second extension axis greater than theminimum radial width of the third flow region about the axis.
 9. Theheat gun as claimed in claim 8, wherein the first and second extensionaxes are symmetrical about the axis, and wherein the first extensionaxis intersects the second extension axis at an included angle greaterthan 60 degrees and smaller than 160 degrees.
 10. The heat gun asclaimed in claim 6, wherein the two flow guiding protrusions include twoouter peripheries converging toward one another in a direction fromoutlet portion to the inlet portion.
 11. The heat gun as claimed inclaim 6, wherein the head portion includes two surfaces disposedoppositely, wherein the two flow guiding protrusions protrude betweenthe two surfaces, and wherein the two surfaces are spaced at a distancegreater than or equal to the width.
 12. The heat gun as claimed in claim11, wherein the two surfaces are inclined from each other such that anincluded angle formed therebetween is greater than 0 degrees and lessthan 10 degrees, and wherein a distance between ends of the two surfaceswhich are adjacent to the inlet portion is greater than a distancebetween ends of the two surfaces which are adjacent to the outletportion.
 13. The heat gun as claimed in claim 1, wherein the first andsecond sides of the first partition are arcuate, wherein the flowpassage includes an annular outlet portion disposed between the inletand outlet ends, wherein the windshield includes a second partitioncooperating with the first partition, wherein the second partition hasopposing first and second sides extending parallel to the axis, whereinthe first side aligns a second phantom line, wherein the first sides ofthe first and second partitions face oppositely, wherein the secondpartition is disposed at the outlet end of the flow passage and in aspaced relationship with the first partition, wherein the first throughhole of the shield is located between first and second phantom lines,and wherein the shield includes a fourth and fifth through hole, withthe fourth through hole located on a right side of the second phantomline, and with the fifth through hole including a portion located on theright side of the second phantom line and a portion located on a leftside of the second phantom line.
 14. The heat gun as claimed in claim 13further comprising an air amplifier for inducing external air flow,wherein the inlet end is formed at an end of the air amplifier.
 15. Theheat gun as claimed in claim 14 further comprising a tube defining theflow passage, wherein the air amplifier defines a channel having a firstopening and a second opening opposite the first opening, with the firstopening having a first radial cross-sectional area about the axis, andwith the second opening having a second radial cross-sectional areaabout the axis smaller than the first radial cross-sectional area.